1. Field of the Invention
This invention relates generally to standing wave electron beam accelerators, and more particularly, to electron accelerators for generating x-ray and electron beams of different energies.
2. Background of the Invention
Standing wave electron beam accelerators have found wide usage in medical accelerators where the high energy electron beam is employed to generate x-rays for therapeutic and diagnostic purposes. Electron beam generated by an electron beam accelerator can also be used directly or indirectly to kill infectious pests, to sterilize objects, to change physical properties of objects, and to perform testing and inspection of objects, such as radioactive containers and concrete structures.
When using an electron beam accelerator for various applications, it is desirable that the generated electron beam has a small cross sectional dimension, and a sharp, well-focused high energy spectrum. It is also desirable to capture as many electrons as possible to thereby reduce current demands on the electron source (electron gun), to bunch the electrons efficiently to obtain desirable spectrum, and to confine the electrons by reducing defocusing effects. This in turn, will result in a generated electron beam that has a desirable output radiation yield. However, existing accelerators may not be able to generate electron beams having all these characteristics. For example, while an accelerator may generate an electron beam having a desirable cross sectional dimension, the output radiation yield associated with the generated electron beam may not reach a prescribed/desirable level.
Also, existing electron beam accelerators generally use external solenoids (or magnets) for focusing a particle beam. Use of external solenoids adds substantial weight to existing accelerators, increases cost of manufacturing, and makes it difficult to maneuver the accelerators (especially when the accelerator is being used to perform testing). As such, it would be desirable to have an electron beam accelerator that does not require external solenoids, while capable of generating electron beam having desired characteristics (e.g., well focused electron beam having high output radiation yield).
Further, many existing accelerators utilize electron sources that use high voltage (e.g., above 50 kV). However, such electron sources increase the size and weight of the overall accelerator, and complicate design and operation of the accelerator. Also, use of injection voltages over 50 kV may require insulation other than air, such as pressurized gas, vacuum, or oil, and use of injection voltages in the range of 20 to 50 kV may require detailing of the accelerator to reduce leakage, corona, and flashover (arcs). Generally, the higher the injection voltage used, the more effort is required to ensure personnel safety. As such, it would also be desirable to have an electron beam accelerator that uses a low voltage electron source while producing a well focused electron beam.